Steel for shaping tools

ABSTRACT

A steel obtained via the metallurgy of a high purity pre-alloyed, agglomerated and densified powder, the steel has the following weight composition: Manganese &lt;1%, silicon &lt;1%, chromium 4.50-6.45%, molybdenum 4-6%, vanadium 6.10-6.5%, tungsten 18.20-18.70%, sulfur &lt;0.0020%, phosphorus ≦0.030%, oxygen ≦100 ppm, cobalt 5-7%, nitrogen 0.050-0.080%, ≦aluminum 0.020%, carbon 1.80-1.95%, balance iron and the impurities which are characteristic of producing steel. The steel has for the most part a dispersion of vanadium MC type carbides.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/FR 97/01328 filed Sept. 17,1997 and based, in turn, on French National application 96 09 080 filedJul. 19 1996.

FIELD OF THE INVENTION

The present invention relates to a steel for producing a shaping tool.

BACKGROUND OF THE INVENTION

As in the aviation, munitions and associated industries, material aremachined still having greater mechanical resistance, it is clear that itis essential to have an extremely hard fast cut steel which, via themetallurgy of the powders, possesses high toughness, thus offeringextremely high level resistance of the positive, cut edges.

OBJECT OF THE INVENTION

The object of the present invention is to provide a fast cut steelproduced initially by powder netallurgy the steel proving to beextremely hard with a scale <<C>>Rockwell hardness of between 68 and 70Rc.

DESCRIPTION OF THE INVENTION

This steel, obtained from a pre alloyed agglometated powder, has thefollowing composition:

    ______________________________________                                        Weight percentages:                                                                        Preferred bracket                                                                           Wide bracket                                       ______________________________________                                        Manganese    0.2-0.40      <1%                                                  Silicon 0.2-0.40 <1%                                                          Chromium 4.50-5 4.50-6, 45%                                                   Molybdenum 4.50-5 4-6%                                                        Vanadium 6.10-6.50 6.10-6.50                                                  Tungsten 18.20-18.70 18.20-18.70                                              Sulphur ≦0.015% ≦0.020%                                         Phosphorus ≦0.020% ≦0.030%                                      Oxygen ≦100 ppm <100 ppm                                               Cobalt 5.40-6.20% 5-7%                                                        Nitrogen 0.050-0.080% 0.050-0.080%                                            Aluminum ≦0.015% ≦0.020%                                        Carbon 1.83-1.90% 1.80-1.95%                                                ______________________________________                                    

Balance: Iron and usual steel-making impurities.

The steel has a dispersed phase mainly composed of vanadium MC typecarbidos. The steel of the present invention possesses remarkabletoughness, due mostly to a particular distribution of primary carbidesassociated with extremely good elevated temperature hardness. Inaddition to the hardness elevated temperature hardness, resistance towear and an exceptional toughness, the family of steels of the presentinvention can be paticuulay adapted to the shaping of toolsmachinability, hardenability and wettability.

The carbon content limited to 1.95% is significant. Beyond this value,the matrix would be rendered brittle. The low oxygen content, less that100 ppm, prevents the oxygen from forming an oxide film on the surfacewhich could create a large network of oxides in the steel followingisostatic compaction. This oxygen content, combined with a nitrogencontent of less than 800 ppm, guarantees `super clean` products.

The stoichiometric relation for forming vanadium carbite (Face centeredCubic MC type) is 1% of vanadium for 0.020% of carbon. The carboncontent of the steel is balanced with its contents of vanadium,chromium, molybdenum and tungsten to provide a sufficient amount ofcarbon and thus enable it to be heat-treated so as to obtain a hardnessof 66Hrc.

According to the invention, the steel for shaping tools possesses acombination of different qualities: resistance to wear, elevatedtemperature hardness characterised by the Mathon cutting capacity test,a toughness not previously having been able to be obtained until now.

Toughness is determined via a measurement according to the Charpy testreferred to in the standard ASTM-23-92 and 23-93. A 10×10×55 mmreference test piece is treated at 1.160° C. stopped in oil or anisotherm stoppage at 560° C., followed by three annealings of one hourat 560° C. It then exhibits a toughness of more than 40 day/cm2. Thecuttin capacity is characterised by the MATHON test (defined in thestandard AFNOR A.03.654).

We claim:
 1. A powder-metallurgy formed from a high-purity agglomerateddensified pre-alloyed powder and having the following weightcomposition:

    ______________________________________                                        Manganese     <1%                                                               Silicon <1%                                                                   Chromium 4.50- 6.45%                                                          Molybdenum 4- 6%                                                              Vanadium 6.10- 6.5%                                                           Tungsten 18.20- 18.70%                                                        Sulfur ≦ 0.0020%                                                       Phosphorus ≦0.030%                                                     Oxygen ≦100 ppm                                                        Cobalt 5- 7%                                                                  Nitrogen 0.050- 0.080%                                                        Aluminum ≦0.020%                                                       Carbon 1.83- 1.90%                                                          Balance iron and usual steel-making impurities.                               ______________________________________                                    


2. The steel according to claim 1 having the following composition byweight:

    ______________________________________                                        Manganese           0.20-0.40                                                   Silicon 0.20-0.40                                                             Chromium 4.50-5%                                                              Molybdenum 4.50-5%                                                            Vanadium 6.10-6.50%                                                           Tungsten 18.20-18.70%                                                         Sulfur ≦0.0015%                                                        Phosphorus ≦0.020%                                                     Oxygen ≦100 ppm                                                        Cobalt 5.40-6.20%                                                             Nitrogen 0.050-0.080%                                                         Aluminum ≦0.015%                                                       Carbon 1.83-1.90%                                                           ______________________________________                                         Balance iron and usual steelmaking impurities.                           